Red vs. Green Scale Inhibitors for Extending Squeeze life—A Case Study From the North Sea, Norwegian Sector—Part II

Abstract

Summary Over the years, environmental legislation has forced changes in the types of scale-inhibitor molecule that can be deployed in certain regions of the world. These regulations have resulted in changes from phosphonate scale inhibitor to polymer-based chemistry, particularly in the Norwegian and UK continental shelf where phosphonates have been either on the substitution list or phased out for many applications. Over the past 10 years, significant improvements in inhibitor properties of the so-called "green" scale inhibitors have been made. However, for one particular operator, the squeeze application of this green scale inhibitor resulted in poorer than expected treatment lifetimes and significant operating cost because of the frequency of retreatment. To overcome the increasing operating cost, an evaluation was made of the current treatment chemicals vs. the older, more-established phosphonate scale inhibitors. The results for the laboratory evaluation suggested that the older chemistry would extend treatment life and reduce operating cost. A case was made to the legislative authority, who approved the use of the phosphonate scale inhibitor, and field applications started. The squeeze lifetimes for the red phosphonate chemistry were shown to be significantly better than the existing yellow/green inhibitors. During the following months, other scale inhibitors with improved environmental characteristics were developed and evaluated. One such molecule was shown to have similar coreflood retention to that of the applied red phosphonate and presented no formation damage. This paper presents the laboratory evaluation of the new scale inhibitor, and illustrates the improvement observed with this new inhibitor through field squeeze-treatment results from a well treated with both the red and new yellow environmental profile inhibitor chemicals. This paper outlines the challenges with environmental legislation and how it has been possible to develop technical solutions (in terms of environmental vs. safety issues and with new inhibitor chemicals) to meet the challenges of offshore scale control.

Impact of Reservoir Temperature on Scale Inhibitor Retention - The Challenge of Ultra-Low Temperature Sandstone Reservoirs

“…The testing carried out to determine the minimum inhibitor concentration required and the coreflood assessment are typical industry standard procedures as outlined in previous publications. (Jordan, 2011;Sørhaug, 2014).…”

“…While the impact of temperature on the performance of scale inhibitors is well documented, less well understood is the impact of low temperatures on the relative retention of scale inhibitors on reservoir rock during scale squeeze treatments. Many case histories are available showing the retention properties of a range of inhibitor types at temperatures greater than 70°C (Jordan, 2011;Sørhaug, 2014;Jordan, 2009), however at temperatures below 70°C less information is available. (Sorbie, 1993).…”

Scale Squeeze Placement Options in Subsea Multi-Lateral Horizontal Wells Completed With Sliding Sleeve Technology

“…The procedure to select a suitable scale squeeze inhibitor is well published (Graham and Collins 2004, Jordan et al, 2011, Sorhaug et al, 2014. In the later life of the well (year 12) the seawater fraction in the produced water has increased to 40% resulting in a higher supersaturation of barium sulphate and increased minimum inhibitor concentration (MIC) from 5ppm to 7.5ppm for the scale inhibitor; also the water cut has increased requiring larger treatment volumes to be deployed to overcome both higher MIC and larger water rates for the same time period of treatment.…”

Selection of Scale Control Strategy on a Sub Sea Developed Field in the North Sea and How 6 Different Companies Contributed

“…Following review of these screening tests, two products (the phosphonate and Polymer C) were selected for core flood testing to further assess their suitability for application in a squeeze treatment in the Blane field. During the period of chemical screening a novel phosphorus-containing polyamine (PCPA) was being evaluated and applied on nearby field also operated by Talisman 22,23,24 and was found to be giving a longer squeeze life than the conventional polymer technology previously applied. This chemical has similar performance to the pentaphosphonate chemical in terms of MED and chemical retention, and so an extra stage of screening was carried out to evaluate if it would be suitable for application to Blane.…”